The color switching accompanied with external bias is defined as electrochromism, where the external bias triggers either a change of molecular stack or electron transfer (redox process). Electrochromic materials that exhibit the necessary colors for RGB and CMYK color replication have been sought after by the display industry for the fabrication of lower-power, thinner, flexible, and less complex displays. Among the numerous types of electrochromic materials, conjugated polymers exhibit high optical contrasts, fast switching speeds, and the multitude of colors achievable through chemical structure modifications. Further, a conjugated polymer, which changes its color by a redox process, has high optical contrast ratio, rapid redox switching, and long-term stability, is a desired material for various electrochromic device applications.
Various colors of the conjugated polymer at the neutral state have been shown, including colors such as blue, green, yellow, and red. However, in some electrochromic device applications, neutral color transitions are desired. A neutral color is a color not associated with any single hue. Some common neutral colors include beige, ivory, grey, taupe, black, and white.
There remains a need in the art for a convenient method for tuning the optical properties of electrochromic devices prepared from conjugated polymers beyond structural modification of the conjugated polymer.